Mattress



FIG. 1 is a front, left side and top perspective view of a mattress showing the new design;

FIG. 2 is a top plan view thereof;

FIG. 3 is a bottom plan view thereof;

FIG. 4 is a front elevation view thereof;

FIG. 5 is a rear elevation view thereof;

FIG. 6 is a left side elevation view thereof; and,

FIG. 7 is a right side elevation view thereof. 

CLAIM The ornamental design for a mattress, as shown and described. 